#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    int waysToStep(int n) {
        if (n == 1 || n == 2)return n;
        if (n == 3)return 4;
        vector<int> dp(n + 1);
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 4;
        for (int i = 4;i <= n;i++)
        {
            dp[i] = ((dp[i - 1] + dp[i - 2]) % 1000000007 + dp[i - 3]) % 1000000007;
        }
        return dp[n];
    }
};